Studies are focused upon the spectrum of circadian changes in the metabolism of bone and cartilage in the growing skeleton. Multiply caged groups of weanling Wistar rats were entrained 2 weeks to a photoperiod of 12 hours (0800-2000 hours) in environmental chambers at a temperature of 21 plus or minus 1 degrees F and 30% humidity. They were then fasted 24 hours. After 24 hours the knee joint synovia were biopsied and the tibias were frozen (17 degrees C), lyophilized, and dissected into cartilage and bone portions for micro- and radiochemical analyses. As expected from previous work, the rates of collagen synthesis were similar at 0900 and 2400 hours in synovia, articular cartilage, metaphyseal and diaphyseal bone, but the growth cartilages retained 2X more C14 when the isotope was administered at 0900 hours. A similar dissociation of rhythms was evident in hexosamine which was richer (3X) in synovia biopsied at 0900 and in the articular cartilages (2X) at 2400 hours. However, the skeletal tissues in the two time groups could not be distinguished by their levels of lysosomal enzymes or enzymes participating in intermediary metabolism.